Prior to the present invention, anion exchangers have been widely used as adsorbents for a variety of ionic substances. As anion exchanging groups, primary, secondary and tertiary amines and quarternary ammonium salts can be cited, but among them, those of the trimethylbenzylammonium type, where trimethylamine is bound with a benzyl group of a polymonovinyl aromatic compound through a covalent bond, exhibit excellent ion exchange ability and are widely used.
However, these trimethylbenzylammonium salt type exchangers gradually decompose even at room temperature and the decomposition speed of the ammonium salt becomes significant especially at 60.degree. C. or higher.
It is therefore impossible to use these at elevated temperatures. Therefore, when a fluid to be treated is at high temperature, the treatment should be performed after the temperature is actually lowered down to 20.degree.-40.degree. C. This wastes considerable energy and reduces efficient ion exchange and adsorption. In addition, there is a serious and annoying defect in that amine is generated by exchanger decomposition even at room temperature giving an unplesant odor. Therefore, an anion exchanger with higher heat resistance is needed.
Disclosure of the Invention
The present invention relates to an anion exchanger having an anion exchanging group of the following chemical formula (I) ##STR2## and a method for treating a fluid using said anion exchanger.
Most of the conventional anion exchangers have an anion exchanging group of the following chemical formula (II). ##STR3## The exchanging group (I) of the present invention exhibits such excellent features that not only the total amount of the exchanging groups is large, but also surprisingly, the heat resistance is high. This is caused by a unique structure of the exchanging group (I).
The maximum working temperature of the conventional exchanging group (II) is 60.degree. C. although it is usually used at 20.degree.-40.degree. C. On the other hand, the exchanging group (I) of this invention is more stable than the conventional exchanging group (II) and can be used at 60.degree. C. or higher.
Therefore, it can be used in such fields where anion exchangers have not been applied previously due to poor heat resistance, e.g. in treating hot ultrapure water and where the working temperature has been unavoidably lowered, e.g. in the field of nuclear reactors and purification of medicines. In addition, as no characteristic odor of amines comes out, it can be also used for treating air and exhaust gas and removing tobacco smoke and other noxious odors. Furthermore, as there is little change with time and decomposed exchanger substance and elute hardly come out, it can be also used as a blood purification material, a filter for analysis and an ion exchange paper.
Therefore, the present invention can contribute considerably to energy saving in these fluid treating fields and achieve high clarification and fine analysis.
In the present invention, as the base body of the anion exchanger, polymonovinyl aromatic compounds and phenolic resins are preferably used. For example, styrene-divinylbenzene copolymer, homopolymers and copolymers of styrene, vinyltoluene etc., phenol resins and blends thereof can be cited. In addition, other polymer components such as poly (.alpha.-olefin) can be incorporated in these polymers as a blend or a composite. Furthermore, graft polymers of a monovinyl aromatic compound such as styrene onto vinyl polymers such as polyolefins, polyacrylates, halogenated polyolefins and flourinated polymers, polysaccharides such as cellulose and cellulose derivatives, polyamides, polyimides, polyesters, preferably in view of chemical resistance poly-.alpha.-olefins such as polypropylene and polyethylene and fluorinated polymers such as tetrafluoroethylene and polyvinylidene fluoride can be cited.
In the exchanging group (I), A.sup.- means a counter anion and is usually OH.sup.-, a halogen anion, BF.sub.4.sup.-, PCl.sub.6.sup.-, and more preferably OH.sup.- or Cl.sup.-. It is possible that a benzene nucleus of a polymonovinyl aromatic compound or a phenol resin can be directly bound with the exchanging group (I) through a direct covalent bond or containing an atomic group, so-called a spacer between them. As the spacer, --(CH.sub.2).sub.n -- (wherein n=1-10), those containing an ether bond such as --CH.sub.2 --O--CH.sub.2 -- and amide bond can be cited.
The anion exchanger of the present invention has usually 0.1 mol or more, preferably 0.2 mol or more exchanging groups based on 1 mol of the benzene nucleus.
When the polymonovinyl aromatic compound is not crosslinked, it is used as a liquid anion exchanger, but it is usually used under a crosslinked and insolubilized condition from the view point of its form retention property. Styrene-divinylbenzene copolymer already has a crosslinked structure. On the other hand, for polymers such as styrene and vinyltoluene, a methylene group, a methoxymethylene group, etc., can be cited as the crosslinking group.
As the physical shape of a crosslinked and insolubilized anion exchanger of the present invention, resin-like (granulated and powdery), filmlike and fibrous (filamentary, short fiber, braided, knitted and woven and paperlike) shapes can be mentioned, but fibrous shapes are preferable considering their relative large surface area and freedom for shape design. A fiber containing a reinforcing polymer, especially a polycore-type composite or mixed fiber where a polymonovinyl aromatic compound is the sheath component and a poly(.alpha.-olefin) for reinforcement is the core component is preferably used from the points of strength and water-permeability.
The method for preparation of the anion exchanger with excellent heat resistance of the present invention is not especially limited and will be explained by using examples as follows.
As a gel type resin and a macroreticular (MR) type resin, which are styrene-divinylbenzene copolymers, and have crosslinked structures, chloromethyl groups are introduced in the aromatic nuclei as they are by conventional means. Furthermore, the chloromethylated resin is treated and reacted with a solution of triethylenediamine of the above structural formula to prepare an anion exchanger of the present invention. Solvents for triethylenediamine include water, alcohols such as methanol and ethanol, hydrocarbon solvents such as benzene and toluene and polar solvents such as N,N-dimethyl-formamide and N-methylpyrrolidone.
On the other hand, the fibrous material is prepared in an islands-in-a-sea configuration in such a way that a polymonovinyl aromatic compound is a main component of the sea component and a poly (.alpha.-olefin) as a reinforcing polymer is an island component. After the fibers are made into a variety of shapes, methylene crosslinking bondings are introduced by treating them with a sulfuric acid solution containing a formaldehyde source to insolubilize the sea component. Then, in the same way as the resin, chloromethyl groups are introduced and furthermore, they are treated and reacted with triethylenediamine to prepare an anion exchange fiber of the present invention.
A method for treating a fluid of the present invention is characterized by using the anion exchanger having the exchanging group (I) as at least one component of an ion exchanger and an adsorbing material. The anion exchanger can be used alone or as a mixture with another ion exchanger or adsorbing material or by using them alternatively. No limitation exists on how to combine it with other ion exchanger and adsorbing materials. As the ion exchanger, cation exchangers having sulfonic acid groups, phosphoric acid groups or carboxylic acid groups, chelating exchangers having aminocarboxylic acid groups, amidoxime groups, aminophosphoric acid groups, polyamine groups, and dithiocarbamic acid groups among others can be cited. As the adsorbing material, active carbon and zeolite can be cited.
The method for treating a fluid according to the present invention can be applied in fields where conventional anion exchangers have been used, e.g. preparation of pure water, water-recycling systems and pure water systems in nuclear power plants and thermal power stations, recovery of useful inorganic anions, decoloring and desalting of sugar solutions, purification and separation of antibiotics and various medicines, purification and separation of amino acids, adsorption of organic bases, adsorption of surface active agents, purification of iodine, adsorption of coloring matters such as dyes, adsorption and removal of proteins, peptides, enzymes, nucleic acids, hormones, alkaloids, nucleotides, lipids, steroids, cells such as bacilli, inorganic colloids such as iron oxide and silica and organic colloids, to name a few. Furthermore, these ion exchangers used where the fluid is a liquid such as water and chemicals, e.g., purification of organic chemicals such as methanol and acetone. In addition, it can be also applied in the fields where the fluid is a gas such as adsorption and removal of an acidic gas such as hydrogen sulfide, hydrogen halide, sulfur dioxide, iodine gas, methyl iodide gas and bad odors.
However, the method for treating a fluid of the present invention can be effectively applied and is especially adapted in fields where application and clarification are difficult with the conventional anion exchangers.
To explain further, in the preparation of ultrapure water, both a cation exchanger having sulfonic acid groups and an anion exchanger are used, but a very small amount of organic substances (TOC) are produced caused by the decomposition of the anion exchanger and this causes a problem in washing semiconductors corresponding to 4M bits or larger. In addition, there is a serious problem in that as the anion exchanger decomposes, part of ion exchanger cannot be sterilized with hot water. Furthermore, from the viewpoint of effective washing, it is required to manufacture continuously hot ultrapure water by means of an ion exchanger. The method for treating a fluid of the present invention can effectively contribute to the preparation of this ultrapure water.
In the treatment of the recycling water in nuclear power plants, both a cation exchanger and an anion exchanger are used, but the real condition is that the recycling water at 100.degree. C. is intentionally and necessarily cooled down to 30.degree.-40.degree. C. because conventional exchangers lack suitable heat resistance and decompose at operating temperatures approaching 100.degree. C. Cooling to a lower temperature causes a tremendous energy loss. The treatment method of the present invention enables treatment at high temperatures and is extremely effective for the treatment of the recycling water in nuclear power plants.
In the purification of highly pure chemicals for the electronics industry chemicals such as methanol, propanol, acetone and hydrogen peroxide water, removal of fine particles and ions at high level are important. But when a conventional anion exchanger is used, decomposition occurs and a very small amount of organic substances (TOC) are generated. From this point of view, the fluid treatment method of the present invention is effective for purification treatment of highly pure chemicals for the electronics industry.
Conventional anion exchangers in the dry form give off a noxious amine odor caused by decomposition is very excessive and it cannot be used for purification of air, and removal of harmful substances in tobacco smoke and other bad odors. No odor is generated by the anion exchanger of this invention so it is effective for efficient cleaning treatment of gases and for this purpose the anion exchanger is formed into air filters, masks, tobacco filters, etc.
In addition, as the change in the anion exchanger with time and eluted substances caused by decomposition of the exchanger is very little and negligable, it is especially useful for analytical treatments and procedures, clean-up and purification of blood when it is used as an ion exchange paper.
As described above, the present invention provides an anion exchanger with a large exchange capacity and excellent heat resistance and secondarily, a significant exchanger for treating fluids.
The present invention is further described and illustrated but not limited by the following examples in which all parts and percentages are by weight unless indicated otherwise.